Field of the Disclosure
The present disclosure, for example, relates to wireless communication systems, and more particularly to techniques for transmitting synchronization signals in a shared radio frequency spectrum band.
Description of Related Art
Wireless communication systems are widely deployed to provide various types of communication content such as voice, video, packet data, messaging, broadcast, and so on. These systems may be multiple-access systems capable of supporting communication with one or more users by sharing the available system resources (e.g., time, frequency, and power). Examples of such multiple-access systems include code-division multiple access (CDMA) systems, time-division multiple access (TDMA) systems, frequency-division multiple access (FDMA) systems, single-carrier frequency-division multiple access (SC-FDMA) systems, and orthogonal frequency-division multiple access (OFDMA) systems.
By way of example, a wireless multiple-access communication system may include a number of base stations, each simultaneously supporting communication for one or more communication devices, otherwise known as user equipments (UEs). A base station may communicate with UEs on downlink channels (e.g., for transmissions from a base station to a UE) and uplink channels (e.g., for transmissions from a UE to a base station).
Some modes of communication may enable communications between a base station and a UE over a shared radio frequency spectrum band, or over different radio frequency spectrum bands (e.g., a dedicated radio frequency spectrum band and a shared radio frequency spectrum band) of a cellular network. With increasing data traffic in cellular networks that use a dedicated (e.g., licensed) radio frequency spectrum band, offloading of at least some data traffic to a shared radio frequency spectrum band may provide a cellular operator with opportunities for enhanced data transmission capacity. A shared radio frequency spectrum band may also provide service in areas where access to a dedicated radio frequency spectrum band is unavailable.
Prior to gaining access to, and communicating over, a shared radio frequency spectrum band, a base station or UE may perform a listen before talk (LBT) procedure to contend for access to the shared radio frequency spectrum band. An LBT procedure may include performing a clear channel assessment (CCA) procedure to determine whether a channel of the shared radio frequency spectrum band is available. When it is determined that the channel of the shared radio frequency spectrum band is available, a channel usage beacon signal (CUBS) may be transmitted to reserve the channel.
When first powering up or establishing communication with a cellular network, a UE may perform a procedure commonly known as acquisition of a cell (e.g., initial acquisition of a cell). When performing acquisition of a cell, a UE may monitor a radio frequency spectrum band for synchronization signals transmitted by a cell (e.g., a base station). Upon receiving a synchronization signal, the UE may determine a timing of a radio frame boundary with which the synchronization signal is aligned. The UE may then synchronize its timing with the timing of the cell, receive other transmissions from the base station, and enter a radio resource control (RRC) connected state with the base station. When performing a cell measurement after acquisition of the cell, a UE may measure the energies of one or more synchronization signals, and use the measured energy or energies, for example, when performing a frequency reselection or cell search. In a dedicated radio frequency spectrum band, synchronization signals may be transmitted and received at predetermined times in every radio frame. However, in a shared radio frequency spectrum band, the transmission of at least some synchronization signals may depend on a base station winning contention for access to the shared radio frequency spectrum band.